DESCRIPTION: Hepatitis C virus (HCV) infection is the leading cause of chronic hepatitis worldwide. Approximately 170 million people are chronically infected and at risk to develop fatal liver damage, such as liver cirrhosis and hepatocellular carcinoma. The core protein represents the putative viral nucleocapsid and influences many cellular functions. Importantly, transgenic mice expressing core accumulate intracellular lipids, a condition called steatosis, and develop hepatocellular carcinoma. We observed that a fraction of core colocalized with mitochondrial markers in core-expressing HeLa and in Huh-7 cells containing the full-length HCV replicon. Using immunoelectron microscopy and in vitro mitochondrial import assays, we showed that core is located on the mitochondrial outer membrane. A stretch of 10 amino acids within the hydrophobic C-terminus of processed core conferred mitochondrial localization when fused to green fluorescent protein. We seek to examine whether the presence of core at the surface of mitochondria directly influences mitochondrial functions. We will generate mutants in the mitochondrial targeting motif and examine their effect on cellular lipid accumulation and apoptosis. Our preliminary experiments show that wild type core markedly induced lipid droplet formation in Jurkat T cells. We further observed a strong proapoptotic effect of core in primary oral fibroblasts after treatment with apoptosis-inducing agents. The interaction of core with several candidate proteins located at the mitochondrial outer membrane will be examined. Potential core targets include carnitine palmitoyltransferase I, a rate-limiting enzyme involved in the uptake of fatty acids by mitochondria, and members of the Bcl-2 family of apoptosis regulators. We anticipate that our studies will help elucidate the mechanisms of how HCV core induces steatosis and hepatocellular carcinoma. [unreadable] [unreadable] [unreadable]